1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus (to be referred to as a CVD apparatus hereinafter in this specification) for depositing various films for semiconductor device and more particularly to a one-wafer processing type CVD apparatus for processing one wafer at a time to deposit various kinds of films on each wafer, one by one, under a condition of a reduced pressure.
2. Description of the Prior Art
In order to form or deposit various kinds of films for semiconductor device by the CVD method, there have been devised and demonstrated an atmospheric pressure cold wall CVD apparatus in which a wafer is heated through intimate contact with a heated wafer carrier and a low pressure hot wall CVD apparatus. These CVD apparatuses are discussed in "Low Pressure CVD Production Processes for Poly, Nitride, and Oxide" by Richard S. Rosler, p.p. 63-70, Solid State Technology, April, 1977 and "Automation in CVD processing", by Richard S. Rosler and Walter C. Benzing, p.p. 27-33, Solid State Technology, July, 1977. In order to realize mass production, both CVD apparatuses employ a batch processing system, so that the same film can be deposited on a plurality of wafer at one time.
In following a recent tendency to use wafers of large diameter, some problems have been encounterd. In the atmospheric pressure cold wall type CVD apparatus, there is a problem that the reactor must be increased in volume to accommodate many wafers, so that the CVD apparatus becomes large in size. In addition, the total sum of the areas of film deposition is increased, it is difficult to uniformly control the temperature of the surfaces of the wafers and the concentration of a reaction gas. As a result, the improvement in uniformity of deposited films is limited. In the low pressure hot wall type CVD apparatus, as the diameter of the wafer is increased, the CVD apparatus becomes large in size. While it was expected initially that uniform films would be deposited, since it is easy to control the temperature in this CVD apparatus, it has been found that except for non-doped polycrystalline silicon it is difficult to deposit uniform films. More particularly, in order to provide uniform films, a boat into which a wafer is loaded and the means for introducing a reaction gas must be specially designed and structured according to every film. As a result, it is difficult to provide a standardized CVD apparatus which has the same structure for depositing various kinds of films.
It can be considered to use the above two types of CVD apparatuses where only one wafer is processed at one time for film deposition, but this process has a disadvantage in that a long time is required to introduce the reaction gas in the atmospheric pressure cold wall type CVD apparatus. In the low pressure hot wall type CVD apparatus, the increase of the partial pressure of the reaction gas and the deposition temperature results in gaseous phase reactions, so that it is difficult to deposit a film at a high deposition rate. That is, the one-wafer processing has a disadvantage in that the throughput is low as compared with the batch processing. As a consequence, there arises a demand for a novel CVD apparatus which does not require a large size, even when the wafer is increased in size; which can deposit uniform films efficiently; and which can deposit various kinds of films without any modification of structure.